This crazy cloud is actually made up of a million dancing birds

The final episode of BBC America's "Planet Earth II" airs on Saturday, March 25.

It's about animals living in the world's biggest cities.

INSIDER got an exclusive look at the episode's sequence on starlings.

They're birds who create breathtaking formations as they fly.

This Saturday, BBC America will air the final episode of the brand-new "Planet Earth II" — a new-and-improved reboot of the 2006 original. The episode is all about the one place on earth you'd least except to find wild animals: cities.

When you think of "Planet Earth," you probably imagine majestic mountains, dense jungles, and remote islands where animals roam free without human intervention. But many of the world's animal species live in harmony with urban-dwelling humans. Noisy, crowded cities offer lots of opportunities for scrappy creatures trying to survive.

The "Cities" episode is easily the series's most beautiful, and it has a fascinating cast of characters: Peregrine falcons that perch on New York City skyscrapers; hyenas that hang with locals in Harar, Ethiopia; and giant catfish that hunt pigeons in Albi, France.

But the episode's most memorable moment features starlings — small black birds that flock to Rome, Italy on winter nights, taking advantage of the city's extra warmth.

Up to a million of them gather in the sky, safety-in-numbers style, to avoid birds of prey. Once there, they perform what looks like a coordinated dance, creating undulating, wave-like formations known as murmurations. BBC America gave INSIDER an exclusive clip of these hypnotic movements. Watch it right here:

The craziest part: Scientists still don't know exactly how or why the starlings do this. They simply dance until, en masse, they fly down to roost in trees for the rest of the night.

Watch the starlings and more urban animals in the "Cities" episode of "Planet Earth II." It airs Saturday, March 25 at 9 p.m. on BBC America.